Voltage injection circuit



Aug. 7, 1956 A. A. MUELLER 2,758,223

VOLTAGE INJECTION CIRCUIT Filed Sept. ISO. 1953 2 Sheets-Sheet 1 All@ 7. 1956 A. A. Mur-:LLER

VOLTAGE INJECTION CIRCUIT 2 Sheets-Sheet 2 Filed Sept. 30, 1953 United States Patent O VOLTAGE INJECTION CIRCUIT Andrew A. Mueller, Arlington Heights, Ill., assigner to C..Nielsen Company, Chicago, Ill., a corporation of mois Application September 30, 1953, Serial No. 383,360

12 Claims. (Cl. 307-137) The present invention relates to what might be termed a voltage injection circuit, and specically is an arrangement for use in connection with low voltage circuits involving switches so that the switch contact resistance will not prevent the switches from functioning properly when they should so function.

The problem of switch contact resistance has existed for years and many attempts have been made to eliminate this problem, particularly in connection with low voltage circuits. For example, contact pressures have been greatly increased or contacts have been made from materials of which the oxides are either physically or chemically unstable or have a resistance not much .different than the contact material itself. Unfortunately, in many low voltage applications where printed circuits and printed switch contacts are employed it is not possible to increase the contact pressure very much. Also, in rotary switching means where a rotating switch arrn successively engages a plurality of contacts and very low voltages are involved, it may be impractical to provide the necessary contact pressure to insure proper contact operation when light contact structure is involved. For a particular applicaf tion involving a particular type of switch with particular contact pressures, it was found that at least sixty volts were necessary to insure proper switch operation unaffected by the contact resistance. There are many applications where voltages as high as sixty volts cannot be used, and it would be desirable to provide an arrangement in which, with voltages much lower than sixty volts, proper functioning of the switch occurs.

Accordingly, it is an object of the present invention to provide an improved means for insuring proper operation of switch contacts in connection with low voltage circuits where the voltages are likely to be lower than the breakdown voltage required for the switch contacts.

It is another object of the present invention to provide an improved voltage injection circuit for insuring proper switch operation in connection with a low voltage circuit.

lt is a further object of the present invention to provide means useful in connection with a multi-contact rotary switch to insure proper contact operation under low voltage conditions.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

Figs. la and lb together comprise a schematic circuit diagram of a system employing the voltage injection cir- 2,758,223 Patented Aug. 7, 1956 ICC charge valve. For the purpose of illustrating the inven tion, a particular application thereof is shown. It should be appreciated that such particular application is by way of illustration and not by way of limitation, since, obviously, numerous other applications will occur to those skilled in the art.

The assignee of the present application for many years has been engaged in determining the listening and viewing habits of wave signal receiver users, so that information with respect to the effectiveness of radio or television advertising can be determined. In a copending application of Charles H. Currey, Serial No. 381,344, led September 2l, 1953, also assigned to the same assignee as the present application, there is illustrated a system for recording the tuning condition of wave signal receivers which employed the voltage injection circuit of the present invention. Since the voltage injection circuit of the present invention has proven to be very satisfactory in such application, it is so illustrated in the instant application.

ln the system described in the above-mentioned Currey application, there was employed a decimal-to-binary converter using linear passive elements without any switch or relay means which resulted in relatively low output voltages for controlling a recording device, which output voltages must be selectively controlled by a rotary commutator switch. This switch requires the voltage injection circuit of the present invention to insure proper operation thereof.

In order to provide a proper background for the use of the voltage injection arrangement of the present invention, it is necessary to include a brief description of the system with which the present invention is associated. Referring now to the drawings, there is illustrated a wave signal receiver 1G, the tuning condition of which it is desired to monitor, so that a record of such tuning condition can be made regardless of the time of day or night during which use of the receiver occurs. Broadly, the

wave signal receiver 10, which is provided With a ground circuit 11 and an antenna 12 as is conventional with such wave signal receivers, is connected by a suitable mechanical link 13 to a receiver attachment 14, which receiver attachment includes a position switch 15 and a decimal-tobinary converter 16. The receiver attachment 14, on the other hand, is connected by a suitable multi-conductor low voltage cable 17 with a recorder 20. This recorder 2G is schematically indicated and includes, among other things, a commutator switch 21, a tilmdrive system 22, a thyratron amplifier 23 for controlling a signal lamp 24 associated with the iilm drive system 21, and a shutter .disc 25 controlling the light from the lamp 24 supplied to the film of the filrn drive system 22. The tuning condition of the wave signal receiver 10 and any other Wave signal receivers which might be involved are converted to electrical signals by means of the position switch 15, which electrical signals are converted from decimal to binary form by the converter 16, whereupon they may be transmitted to the recorder 20 and suitably recorded.

The wave signal receivers which are being monitored may be of any form and the illustrated receiver 10 has merely been schematically indicated in the drawings. In addition to the antenna ground circuit already described, the receiver l), which may be one for amplitude modulated or frequency modulated signals or both, which signals are convertible to visible or audible form or both,

is provided with a signal reproducer 28. This signal reproducer 28 has been schematically illustrated as a loud speaker, although, obviously, it might equally well comprise a fluorescent screen or similar apparatus. interposed between the antenna ground circuit comprising the antenna 12, the ground connection 11 and the signal re producer' 28, are, of course, the usual stages of a wave signal receiver which are not shown but which might com- 3 prise a tunable radio frequency amplifier, a mixer or modulator, and, in the case of a conventional radio receiver, an audio frequency amplifier and the like. Since the wave signal receiver lll is representative of vany conventional receiver, whether it be radio receiveror a television receiver, its mode of operation will readily be apparent to those skilled in the art, and, consequently, no further discussion thereof is included in this application.

si/ave signal receivers generally include some form of tuning apparatus, and for Wave signal receiver this is schematically designated vby the reference numeral 3% in Fig. la of the drawings, comprising a tuning lknob 31 and a resonant frequency varying device 32 vdrivingly interconnected by a tuning shaft. The wave signal receiver il@ also includes a power supply unit 34, which power supply `unit is suitably connected to a power out-- let through a conventional power cord 35 having at the end thereof the ordinary plug connector 36. The energization of the wave signal receiver llt is conventionally controlled by a set switch 33 which usually is combined with the manual volume controlmeans.

For ythe purpose of supplying power to the receiver attachment i4, there are included a pair yof 4power ysupply conductors 39 leading from the power supply unit 34 of the receiver 10 tothe receiver attachment 14. Inzorder to make sure that the recorder isfconnected to the receiver l@ so that all use `of tle receiver is recorded at all times, one lead of the .power cord ,35 is completed only if a plug connector 4t) in the receiver attachment 14 connects the recorder 2t) ywith the receiver attachment 14. This connector tu is illustrated as a multi-prong connectcr, two prongs of which interconnect the conductors 41a and 41!) to complete the power circuit to the power supply unit ,34 of the receiver llt). This is a feature to insure that the receiver attachment M is electrically connected to the recorder 2t? before the receiver l() can be operated. lt will be apparent that with the arrangement shown in the drawings, no current can tlow'in conductors 35 when the plug connector 4d is disconnected, even though set switch 33 is closed.

For the purpose of converting the tuning position of the tuning shaft 33 of the receiver lil to a readily transmittible indication such as an electrical signal, there is provided in the receiver attachment ldthe position switch 15, described above, which may he of the yform disclosed and claimed in copending Krahulec application, Serial No. 78,926, tiled March l, 1949, and assigned to the rsaine assignee as the present application. Essentially, the position switch l5 comprises a rotary conducting `shaft 43 lto which are attached a yplurality lof regularly yspaced .cams 44a, 44h-134C, 44d, 44e, Lief, lli-g, 44h, 4st, 44]', 44k, 44m, dan, 44p and 44g. A s illustrated, there areiifteen earns d4. Each of these cams da includes an identical raised portion for making electrical contact with `an associ- .ated contact d5 designated by the same subscript as the contacts '44. Thus, the cam dlicat a. predetermined point during the rotation thereof will engage its associated contact 45a. Similarly, the cam rif/ib at a predeterminedpoint in its rotation will contact its associated contact lib'ib, .and

so on with the remainder of the cams andthe associated contacts45.

Preferably, the cams dit are adjustable relative to the shaft 43 so as to engage their associated contacts ,4S in any desired predetermined sequence. Likewise, the position switch l5 preferably includes the features disclosed and broadly claimed in Rahmel Patent No. 2,484,734,

whereby each cam 44 will engage its associated contact d5 over the entire position of the tuning shaft C93 that a particular transmitting station can be tuned in. It will be understood that the angular extent over which this can occur will vary, depending upon the particular station involved, as is fully disclosed in the above-mentioned Rahmel patent. Although there have been disclosed fteen cams 44, yall connected to the same kconducting shaft 43, which would be capable of giving indication tor il fteen separate tuning channels, it will readily be appreciated that more or less cams could be employed and, as a matter of fact, some of the cams might be used to indicate tuning to a frequency modulation band, while others might he used to indicate `tuning to an amplitude modulation band. Fifteen cams have been found to be entirely ladequate to cover the ordinary listening to which a particular radio receiver is subjected, since there usually are not that many stations that can be received satisfactorily, ror at least that are commonly tuned in. In the case of television receivers, there are presently only a maximum of seven channels available to any one receiver. lt will be obvious that the cams dit will Depositioned on the conducting shaft 43, so that the associated contacts 45 are sequentially engaged as the tuning shaft 33 is caused to scan the frequency spectrum of receiver 10.

For the purpose of correlating the position of the tuningshaft '33 and the shaft d3 of the position switch l5, the mechanical link i3 is provided, which could comprise a. pair of Bowden wires a7, the ends of which are preferably Wrapped around the respective shafts 33 and 43, or around suitable pulleys such as /l and 49 associated with such shafts. As illustrated, the pulley 43 is mounted on Athe shaft 33, whicc the pulley 49 is drivingly connected to the position switch shaft through a pair of gear Fmembers 5@ and Si. it will be apparent from the above description that thc cams fifi may be individually adjusted so as to complete an electrical. circuit with an associated Contact 45 whenever the tuning shaft 33 is tuned to a particular transmitting station of which the particular-'cam 44 is representative.

The power supplied through conductors 39 to the rcce'iver attachment ld is supplied to a suitable current limiting yand voltage isolating transformer 54, having a primary Winding 53 and a secondary winding 55. The transformer Si@ is so arranged that even with a dead short Vcircuit across the same no tire hazard is involved. The .conductors 39 are indicated as being connected tothe primary winding One terminal of the secondary winding 55 `is indicated as being connected to the position switch .conducting shaft 43 through a noise suppression resistor 5d and a collector ring 57 which continuously engages a suitable brushlike Contact member 58. The :other terminal of the secondary winding 55 is connected `throughaconductor dit with the decimal-to-binary converter i6. Suitable noise suppression capacitors 6l., 62 and 63 are also associated with the transformer 54 in conventional manner.

To produce a recordable indication of the on and foff condition of the receiver il), there is provided a voltage divider comprising resistance elements 64 and 65 connected across the secondary winding 55 o'f the transformer 54. Whenever the receiver it) is turned on,

a potential will appear across this voltage divider, which potential -is supplied to a conductor 67, which, with the 'conductor connected :to the conductor di), is included 4inithe cable ll7 leading to the recorder 20 as described in greater detail hereinafter.

Thus, the conductor 67 provides at the recorder an indication of the wave signal receiver on condition `at all vtimes when lthe receiver vis turned on,.even though it may not be tuned to a staltiondor-whichone of the cams 44 is speciiically provided. The decimal-to-hinary converter 16 fully disclosed and ,claimed yin the above-mentioned Culrey appiication is specifically illustrated as kone for converting a decimal fifteen representation lto a binary four representation. The particular construction of the decimal-to-binary converter '16 fforms no part of the present invention. Briefly,

however, ,this lconverter 16 includes `iifteen separate conductors on the input side designated as -70 with an approypriate fsubscript corresponding to the subscripts of the These four conductors are designated as 71a, 71b, 71e and 71d. The decimal conductors 70 and the binary conductors 71 are interconnected in a suitable manner by linear passive elements comprising resistors 72 to 95, inclusive, and 97 to 104, inclusive, collectively designated as the resistors R. Thus, the application of a voltage to any one of the fifteen input conductors 70 causes a unique combination of potentials on the four output conductors 71. The voltages on the output conductors 71 are taken in two groups: those designated undesired which are below some maximum value, and those designated desired which are at least three times greater than said maximum value. There are fifteen different combinations or permutations of desired and undesired voltages. Thus, if a potential is applied to any one of the fifteen input conductors, there is a unique combination of voltages at the output conductors to identit'y which input conductor was so energized. Actually, the fteen input conductors are arranged in an orderly system and are specifically illustrated as the horizontal conductors of a grid or matrix. The resistors interconnecting the input conductors and the output conductors which are arranged as the vertical conductors of the grid, are interconnected by the resistors R. In order to provide the desired combination of voltages on the output conductors, the output conductors are indicated as each bearing code numbers 1, 2, 4 and 8, respectively. The sum of the code numbers of the particular conductors energized at any time will give equal decimal representation of the decimal conductor energized. Between each output conductor and ground there is connected a resistor "r" specifically designated in the drawings as resistors 106, 107, 108 and 109. Each of these resistors r has a value approximately one-tenth the value of resistors It will be noted that a desired voltage is obtained on output conductor when a resistor R is connected directly between that conductor and the energized input conductor, and that an undesired voltage is obtained at the output conductor by reason of the fact that there are other indirect paths between the output conductor having an undesired voltage and the energized input conductor, said paths comprising several resistances R in series parallel combination. It will, thus, be apparent that if an appropriate output voltage is obtained across various combinations of the binary digit conductor 71, a code unique to fifteen stations can then be obtained from the four conductors.

To complete the energization circuit of the matrix defining the decimal-to-binary converter 16, each of the resistors 106, 107, 108 and 109 is connected to the conductor 60 and, hence, to one terminal of the secondary winding 55 of the transformer 54. This conductor 60 is grounded as indicated at 114. Thus, one terminal of all the resistors 106, 107, 108 and 109 is grounded, and the other terminals of these resistors Aeffectively comprise the sources of output potential of the decimal-to-binary converter 16. Accordingly, these output terminals ot' the resistors 106 to 109, inclusive, are connected to the recorder by suitable conductors included in the cable 17. As illustrated, the outpu-t terminal of the resistor 106 is connected to a conductor 110. The output terminal of the resistor 107 is connected to a conductor 111. The output terminal of the resistor 108 is connected to conductor 112, and the output terminal of the resistor 109 is connected to a conductor 113. It will be apparent that whenever one of the cams 44 engages its associated contact 45, an output voltage will appear across some or all of the resistors 106, 107, 108 and 109, assuming, of course, that the transformer 54 is energized. The output voltage of the decimal-to-binary converter is an alternating current voltage in the neighborhood of between fifteen and twenty volts, and it is quite obvious that this low voltage can readily be carried in the cable 17 which may be run along the baseboard of the home orl concealed in any manner without presenting any fire or shock hazard. Such low voltage is very desirable from the standpoint of eliminating any lire or shock hazard, but presents a problem in the recorder 20, as will become apparent from the following description.

To eliminate any undesirable noise and to act as noise Suppressors, suitable capacitors 115, 116, 117, 118 and 119 are included in the decimal-to-binary converter 16. These capacitors are connected between ground and the output conductors 67, 110, 111, 112 and 113, respectively.

The functioning of the decimal-to-binary converter 16 forms no part of the present invention, and the only thing which is important as far as the present invention is concerned, is that a low voltage output is obtained between fifteen and twenty volts. To record in binary code the low voltage signals at the output of the binary converter 16, this information is supplied' to the recorder 20, which recorder includes the commutator switch 21, the film drive system 22, the thyratron amplifier 23, the signal light 24, and the shutter disc 25. The hlm drive system 22 may include any medium upon which a record is produced. ln order to simplify decoding the recorded information, it is preferably recorded on photographic film, a small portion of which is designated by the reference numeral 143 in Fig. 1b of the drawings. lt should be appreciated that as far as the present invention is concerned the recording medium 143 need not be photographie film. However, photographic film does lend itself well to high speed decoding and has numerous other advantages. The film 143 is illustrated in Fig. lb of the drawings as movable over a suitable guide pulley 144.

lt will be appreciated that the signal light 24 is provided to exposed selected portions of the film 1li-3, and suitable lenses 145 and 146, a target 157, and the shutter disc 25 are interposed in the light path between the light source 24 and the film 143. To insure long life, the signal light or lamp 24 is preferably an argon lamp, in which case it would be connected in series with a suitable current limiting resistor 158. This lamp 24, as will become apparent from the ensuing description, must be connected across a suitable power circuit and controlled by the commutator switch 21 in order to produce the desired control thereof. When the light is energized, it will produce a record indication on the film 143. By employing the decimal-to-binary converter 16 described above, which has a relatively low output voltage, there is not suiiicient voltage available to energize the lamp 24, such a lamp normally requiring voltages of the order of ninety volts or thereaoout, There-- fore, the thyratron amplifier unit 23 is provided to insure that the low voltage output from the decimal-tobinary converter 16 can properly energize the llamp 24 at the appropriate times. The lamp 24 will be energized at least once per minute, and sometimes several times per minute; and to avoid any radio interference, suitable lter means and noise suppressor circuits are provided, which include the capacitor and resistor elements already described. 4

For the purpose of causing the lamp 24 to expose certain portions of the film 143 in a predetermined manner so that binary code indications are produced in correct positions across the record receiving element 143, it is necessary to expose predetermined transverse portions of the film 143 in synchronisrh with the energization of the light source 24. The optical system already described, including the light source 24, is therefore provided, of which the shutter disc 25 is a very important element.

To properly correlate the shutter disc 25, which is a rotatable element, with the cornmutator switch 21, the two are preferably driven at one revolution per minute by the same motor which is illustrated as being directly connected by a common shaft 161 with the rotating arm`162 of the commutator switch 21, and also connected with the shutter disc 25. In order to cause asesinas the light 'from the l'source T24 Ato 'fall on different vpredetermined positions transversely ,of ythe liilm y143 in dependenceupon the :pulses produced bythe commutator switch 21, the rotating shutter disc 25 is provided with a plurality of elongated slitstor openings 164. The slits 164 are arranged in a spiral around the disc thereby to cause the light to move'successively across the film 143. Thus, the slits are successively presented to vthe light source 24 so `that the iilm is exposed transversely beginning with one side and moving to the other. Preferably suitable means are provided to move the tilm 143 the width of one of the slits in the shutter disc during the time that the 4disc `rotates fthrough one revolution, so that vthe record will always be produced on an unexposed portioniof the film. The shutter disc25 is also provided with one large-opening 165 to permit the held man to view the entire film for initially adjusting the optical system. In initially adjusting the optical system of the recorder 2t), the commutator switch 21 would be adjusted so that a particular contact thereot` was energized or at least was engaged by rotating contact arm 162 when a particular slit 164 of the shutter disc 25 was effective to transmit light from lamp 24 to hlm 143. The motor 16() is connected to a source of power not shown by suitable power conductors 166 and the conventional plug connector 16611.

The commutator switch 21 is a very simple type of switch having a rotating switch arm 162 capable of successively engaging a plurality of contacts 167, and specifically designated as 167e, 167b, 167C, 167d, 167e, 1671, 167g, 16711, 167i and 167]'. Actually, ten contacts are illustrated, although a greater or lesser number can readily be employed. For producing a record of the tuning condition of the receiver lil, only six contacts 167a to 167f, inclusive, are indicated as being used. Actually, additional contacts may be employed for additional time information and the like, and also additional contacts may be included in the commutator switch 21 to take care of additional receivers if more than one receiver is being logged by the recorder 2l). As illustrated, in Fig. lb, the conductor 68 in cable 17 is grounded at the commutator switch 21, while the conductor 67 is connected to the contact 16711, the conductor 110 to the contact 167C, the conductor 111 to the contact 167d, the conductor 112 to the contact 167e, and the conductor 113 to the contact 1671. The commutator switch 21 may comprise any suitable type of rotary switch, and, since the contact arm 162 rotates at one revolution per minute and low voltages are involved, relatively low contact pressuresl are employed. The switch might be one referred to as a printed circuit switch, or it might comprise any other switch. In a switch utilized in the above system including the voltage injection circuit of the present invention, silver switch contacts were employed.

To provide a source of power for various purposes in the recorder 20, there is connected to the power conductors 166 a suitable transformer 170 having its primary winding 171 connected in parallel with the motor 164i. The secondary winding 172 of the transformer 171 is a center tapped winding, the center tap of which is maintained at ground potential by virtue of its connection through conductor 173 to ground connection 174. The other terminals of the secondary winding 172 are connected through suitable rectiiiers 175' to a common terminal 176 which edectively comprises the positive rectitier output terminal. Actually, the output voltage at the terminal 176 comprises an unfiltered full wave rectiiier voltage which is sometimes termed a folded alternating current voltage wave which is essen-.tial for proper operation of the thyratron amplifier 23 forming no part of the present invention but disclosed and claimed in the above-mentioned Currey application. Such a folded alternating current voltage output at terminal 176 is supplied to the plate circuit of the thyratronampliiier 23, so that it is immaterial what the phase of the signal from .the receiver attachment might be; in other words,` so that it `ispimniaterial vhow the plug connector 36 is` plugged into the socket. A vtrue direct vcurrent plate voltage for the thyratron amplifier 23 would eliminate the polarity .problem, but would have the disadvantage that there would be no voltage zero provided to extinguish current :ow through the thyratron amplifier dcscribed hereinafter.

:It will be appreciated that `in addition to providing a lrecord of the tuning condition of the receiver 10, suitable time information should also be applied to the film 143 simultaneously with the tuning information. Elaborate vmeans for providing such time information are vdisclosed in the above-mentioned Currey application. This has not been illustrated in the drawings except that minute marks are applied by virtue of the contact 167e. the commutator switch 21. This is accomplished by connecting the contact 167a -with one terminal of the secondary winding 172 through a suitable voltage dropping resistor 177 and a conductor 178. Thus, an alternating potential is continuously applied to the contact 167a at all times, and once each minute when the rotating contact arm 162 engages contact 167:1 a potential is availble for energizing the lamp 24.

As was pointed out above, the relatively low output voltages of the decimal-,to-binary converter 16 necessitates the use of suitable amplifying means between these output voltages and the lamp 24, which amplifying means are illustrated as the thyratron amplifier 23. This ampli- "tier is `illustrated as comprising an electron discharge valve 179 having an anode 180, a cathode 181, a. control electrode 182, and a Shield grid 183. The plate circuit, including the anode 180 of the discharge valve 179, is connected through the current limiting resistor 158 to one terminal of the lamp 24, while the other terminal of the lamp 24 :is connected to the terminal 176 of thc folded alternating current voltage source. For establishing a predetermined cathode bias, the cathode 181 of the electron discharge valve 179 is connected to ground 174 through a suitable tixed resistor 184 and an adjustable resistor 18S, and through the series resistors 186 and 187 to the positive terminal 176, the resistors 184, 185, 186 and 187 forming a voltage divider network between terminal 176 and ground 174. The shield grid 183 is connected to the cathode 181 through a suitable currentlimiting resistor 188. The control electrode 182 of the thyratron amplifier 23 is connected through a suitable resistor 196, a control switch 191, and a resistor 192 with the rotating arm 162 of the commutator switch '21. When the switch 191 is closed, as indicated in Fig. lb of the drawings, the potentials applied to the contacts 167 when engaged by the rotating contact arm 162 will be applied to the control electrode 182. For example, when the rotating switch arm 182 engages the contact 167e to which a constant alternating potential is applied through conductor 178, a potential will be applied to the control electrode 182 causing the thyratron 179 to fire once each minute as the switch arm 162 engages contact 167e. The resistor 185 is adjusted for the proper setting, so that the undesirable voltages obtained from the decimal-to-binary converter 16 will not cause the thyratron 179 to tire.

It was pointed out above that the voltage output of the decimal-to-binary converter 16 was a relatively small voltage, often less than twenty volts alternating potential, which means that it would have a somewhat higher peak voltage. Actually, the peak voltage output was found never to exceed thirty volts. The present invention is concerned primarily with means for eliminating any problem o'f failure to break down any resistance lm between the rotating contact arm 162 and the contacts 167 under such low voltage conditions. As was pointed out earlier, a voltage of the order of sixty volts is necessary to make sure that this contact film always breaks down. It will be apparent that vif contact resistance prevents current from iiowing through the contact arm V162, an incorrect record will be applied to the film 143. Thus, in accordance with the present invention, there is provided what is termed a voltage injection circuit whlsh applies a predetermined high direct current potential to the switch contacts of the commutator switch 21.

For the particular application described above Where the voltage from the decimal-to-binary converter supplied to the commutator switch 21 is between fifteen and twenty volts alternating current with a peak value never exceeding thirty volts, it is essential that the voltage injection circuit of the present invention supply a sufficient voltage to the contact 167 to make sure that under every condition at least sixty volts plus a suitable factor of safety will be applied to the contacts. Since it is possible for a voltage in a negative direction having a peak value of the order of thirty volts to be applied to the contacts 167 which would subtract from the voltage applied by the voltage injection circuit, it is essential that a voltage suiciently high be applied, so that even when subtracting the voltage peak applied by the decimal-to-binary converter 16 there would still be an excess of sixty volts. For the application illustrated, the voltage injection circuit is designed to provide one hundred volts negative direct current to the contacts 167, so that even if a peak of thirty volts in the opposite direction were applied to these contacts 167, at least seventy volts would be available to break down the resistance film. To this end, a suitable voltage divider comprising resistances 196 and 197 are connected between one terminal of the secondary winding 172 of the transformer 170 and ground 174. Also, by means of rectifier 198 a high negative potential of the order of 100 volts is obtained at a terminal 199. A suitable smoothing capacitor 20% is connected between terminal 199 and ground 174. This high negative potential is connected by means of a conductor 201 and a high voltage dropping resistor 202 to the rotating contact arm 162 through the switch 191 and the resistor 192.

In order to make sure that this high negative voltage of the order of one hundred volts disappears insofar as its effectiveness or control on the thyratron amplifier is concerned as soon as the contacts of commutator switch conduct current or, in other words, as soon as there is assurance that the contact lm is broken down, the resistance 202 is designed to have a resistance value about one thousand times greater than the resistance of resistor 192. For the particular application illustrated, the resistor 192 had a resistance. of about the order of magnitude of the output impedance of decimal-to-binary converter 16, which means that the resistor 292 had a value of at least five hundred times the remaining impedance of the circuit in which it is connected. Thus, as long as no current flows through the rotating contact arm 162, a relatively high negative voltage is applied tothe rotating contact arm 162, which adds to the voltage applied by the decimal-to-binary converter in the event that the alternating current voltage is positive or is reduced in value in the event that the output of he decimal-to-binary converter is in the other half cycle, Since the sum of these voltages, considering peak value of the alternating current, is between seventy and one hundred thirty volts negative, as the case may be, breakdown is assured in every case, since extensive tests have demonstrated that sixty volts are ample to break down the contact resistance. Just as soon as any current liows through the contact arm 162, however, the drop across the resistor 202 is so large that only a very small voltage, actually but a small fraction of the output voltage of converter 16, is applied by the voltage injection circuit to the control electrode 182 of the thyratron amplifier 23, so as not to interfere with the operation of thyratron 179.

In View of the detailed description included above, the operation of the voltage injection circuit of the present invention will readily be understood by those skilled in the art. It will be appreciated that even though a very small voltage is applied to the contacts of a switch, with 10 the injection circuit of the present invention a sufiiciently large voltage is available to insure breakdown of any oxide film which might exist. Moreover, with the present invention this means insuring that contact film` resistance breakdown in no way interferes with the operation of the thyratron amplifier.

While there has been illustrated and described a particular embodiment of the present invention, it will be apparent that various changes and modifications will readily occur to those skilled in the art. Accordingly, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and. scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is;

l. In combination, a control switch having a pair of relatively movable contacts for making and breaking an electric circuit, means for applying a signal of relatively low power across said contacts, a source of relatively high potential, and a circuit for applying the output of said relatively high potential source in series with said low power signal across said contacts to break down the contact resistance.

2. In combination, a control switch having a pair of relatively movable contacts for making and breaking an electric circuit, means for connecting said contacts to the control electrode of an electron discharge valve, a source of relatively high potential and a circuit for applying momentarily the output of said relatively high potential source across said contacts in order to break down the contact resistance.

3. In combination, a control switch having a plurality of fixed elements and a movable element adapted to successively contact the fixed elements, means for applying a signal of relatively low potential through the contacting elements, a controlled circuit responsive to said signal, a source of relatively high potential, a circuit for applying the output of said relatively high potential source across said contacting elements simultaneously with the application of' said low potential signal to break down the contact resistance, and means for preventing said high potential source from atecting the response of said controlled circuit as soon as the contact resistance is broken.

4. In combination, a control switch having at least one movable contact arm and a plurality of fixed contacts, means for applying signals of relatively low potential to said iixed contacts, a circuit energized by said signals, means for continuously applying a relatively high potential signal to said movable arm to insure the breakdown of contact resistance between said xed contacts and said movable arm, and means for preventing said high potential signal from affecting the energization of said circuit as soon as the Contact resistance is broken.

5. In combination, a control switch having a plurality of fixed contact elements and at least one movable contact element for contacting said fixed elements, means for applying signals of relatively low potential to the contacting elements, a circuit responsive to said signals, and means for continuously applying a relatively high potential to said movable contact element to insure the breakdown of contact resistance between each of the contacting elements, said last named means including a voltage divider network comprising a plurality of irnpedances, at least one of said impedances being larger than the others, said circuit being energized by the signals developed across the larger of said impedances thereby rendering the circuit unresponsive to said relatively high potential as soon as the contact resistance is broken.

6. In combination, a control switch having a plurality of fixed elements and a movable element adapted to successively contact the xed elements, means for applying a signal of relatively low potential through the contacting elements, a source of relatively high potential signals, and means for applying the output of said relatively potential source across said contacting elements simultaneously with the application of said low potential signal to break down the contact resistance, said last named means including a voltage divider comprising at least two impedances of diierent size connected in series with said high potential source and said contacting elements for causing said low potential signal to appear substantially across the larger of said impedances, and a circuit responsive to the signal developed across the larger impedance.

7. In combination, a control switch having at least one movable contact arm and a plurality of fixed contacts, means for applying signals of relatively low potential to said iixed contacts, a circuit adapted to respond to said signals when said movable arm contacts said fixed contacts, means for applying a relatively high potential to said movable arm to insure the breakdown of contact resistance between said fixed contacts and said movable arm, said last named means including a pair of impedances connected in series, one having a value considerably larger than the other, said circuit being energized by the signals developed across the larger of said impedances thereby rendering the circuit unresponsive to said relatively high potential as soon as the Contact resistance is broken.

8. In combination, a control switch having a plurality of fixed members and a movable member adapted to successively contact the fixed member, means for applying a signal of relatively low potential through the contacting members, a discharge tube including a control element responsive to said low potential signal, a source of relatively high potential signals, a circuit for applying the output of said relatively high potential source across said contacting members simultaneously with the application of said low potential signal to break down the contact resistance, means for connecting the control element of said discharge to said circuit, and means for rendering said tube unresponsive to the output of said high potential source as soon as the contact resistance is broken while at the same time rendering said tube responsive to said low potential signal.

9. In combination, a control switch having a plurality of fixed members and a movable member adapted to successively contact the fixed members, means for applying a signal of relatively low potential through the contacting members, a discharge tube including a control element adapted to respond to said low potential signal, a source of relatively high potential signals, a circuit for continuously applying the output of said relatively high potential source to said movable member in order to break down the contact resistance when the fixed and movable members contact, means for connecting the control element of said discharge to said circuit, and means for rendering said tube unresponsive to the output of said high potential source as soon as the contact resistance is broken while at the same time rendering said tube responsive to said low potential signal.

l0. In combination, a control switch having a plurality of fixed members and a movable member adapted to successively contact the fixed members, means for applying a signal of relatively low potential through the contact- Iing members, a discharge tube including a control element adapted to respond to said low potential signal, a source of relatively high potential signals, a circuit for applying the output of said relatively high potential source across said contacting elements in series with said low potential signal to break down the contact resistance, said circuit including a pair of impedances of different size connected in series with said source and said contacting members, means for connecting the control element of said discharge tube across the larger ot said impedances, the output of the high potential source appearing at said control element before the contact resistance is broken and being sufiicient to cut oit said tube and the potential appearing across the larger impedance as soon as said contact resistance is broken being related in magnitude to said low potential signal.

ll. In combination, a control switch having a plurality of fixed elements and a movable element adapted to successively contact the fixed elements, means for applying a signal yof relatively low potential through the contacting elements, a source of relatively high potential, and a circuit for applying the output of said relatively high potential source in series with said low potential signal across said contacting elements to break down the contact resistance.

12. In combination, a control switch having a plurality of fixed elements and a movable element adapted to successively contact the ixed elements, means for applying a signal of relatively low potential through the contacting elements, a source of relatively high potential and a circuit for applying the output of said relatively high potential source across said contacting elements simultaneously with the application of said low potential signal in order to break down the contact resistance.

References Cited in the file of this patent UNITED STATES PATENTS 1,785,818 Peterson et al Dec. 23, 1930 2,183,838 Hornickel Dec. 19, 1939 2,647,165 Buchner July 28, 1952 

